1. Field of the Invention
The present invention relates to a system for detecting fire or overheating.
2. Description of the Related Art
A variety of different systems and methods for detecting fire or overheating are known. These systems are often used in engine regions, for example, of an aircraft, ship, helicopter, submarine, space shuttle or industrial plant, and more generally in any sensitive region where the risk of fire or overheating exists, for example, in a hold or bunker, train compartment or boiler.
U.S. Pat. No. 5,136,278 describes one type of detector that detects local or average overheating. The detector uses a gas which, when it expands owing to the effect of overheating, trips an electrical contact, thereby indicating that a mean temperature of the detector has exceeded a threshold temperature. Metal oxides with an absorbed gas distributed over the entire length of the detector provide, by a degassing principle, a local indication that the temperature exceeds the threshold temperature.
Another type of detector measures the resistance of a material having a negative thermal coefficient (“NTC”). The material may be implemented as a negative thermal coefficient cable. This type of detector is used for detecting local overheating.